Microfabrication techniques were originally developed for the microelectronic industry, researchers have been able to create simple designs such as well-defined and repetitive patterns of grooves, ridges, pits, and waves. Techniques such as photolithography, electron-beam lithography, colloidal lithography, electrospinning, and nanoimprinting are popular methods for fabricating micro and nano topographical features. The need for large capital investments and engineering expertise has prevented the widespread use of these fabrication methods in common biological laboratories.
Studies of cellular responses to topographies ranging from nano- to microscales are of great importance to fundamental cell biology as well as to applications in stem cell biology and tissue engineering. (Chen, C. S. et al. (1997) Science 276:1425; Dalby, M. J. et al. (2007) Nat. Mater. 6:997; Kim, E. A. et al. (2010) Proc. Natl. Acad. Sci. USA 107:565) Leveraging traditional fabrication techniques originally developed for the semiconductor industry, researchers have been able to precisely control the topographical features of in vitro substrata to better understand the interaction between cells and their microenvironments. Previous studies have demonstrated the phenomenon of contact guidance, directed alignment and migration along lines of topographic anisotropy, using a variety of cells—from myocytes to adult stem cells—with a range of responses. (Kim, E. A. et al. (2010) Proc. Natl. Acad. Sci. USA 107:565; Dalby, M. J. et al. (2003) Exp. Cell Res. 284:274; Nathan, A. S. et al. (2010) Acta Biomater. 7:57; Watt, F. M. et al. (1988) Proc. Natl. Acad. Sci. 85:5576) For example, the effects of contact guidance have been shown to induce cytoskeletal rearrangement, nuclear deformation, and gene expression changes in fibroblasts. (Dalby, M. J. et al. (2003) Exp. Cell Res. 284:274) In addition, stem cell fate can be solely determined by the mechanical cues of their microenvironment in the absence of soluble factors. (Watt, F. M. et al. (1988) Proc. Natl. Acad. Sci. 85:5576; Engler, A. J. et al. (2006) Cell 126:677; Murtuza, B. et al. (2009) Tissue Eng. Part B Rev. 15:443; Pagliari, S. et al. (2011) Adv. Mater. 23:514; Solimon, S. et al. (2010) Acta Biomater. 6:1227) Therefore, the substrates used for such studies need to be biologically relevant and mimic the in vivo microenvironment.
While it has been shown that biophysical cues of various length scales affect cells differently, (Dalby, M. J. et al. (2007) Nat. Mater. 6:997; Kim, E. A. et al. (2010) Proc. Natl. Acad. Sci. USA 107:565; Dalby, M. J. et al. (2003) Exp. Cell Res. 284:274) the majority of currently available fabricated topographies have simple and repetitive patterns of grooves or ridges of either a homogenous size or of a narrow size range at either the microscale, or more recently, the nanoscale. (Chen, C. S. et al. (1997) Science 276:1425; Nathan, A. S. et al. (2010) Acta Biomater. 7:57; Yim, E. K. et al. (2010) Biomaterials 31:1299; Yim, E. K. et al. (2010) Biomaterials 31:1299; Bettinger, C. J. et al. (2009) Angew. Chem. Int. Ed. 48:5406; Bowden, N. (1998) Nature 393:146; Lam, M. T. et al. (2008) Biomaterials 29:1705; Jiang, X. et al. (2002) Langmuir 18:3273) Although such designs are helpful in studying a controlled cellular behavior, they do not represent the physiological conditions of native tissue necessary for tissue engineering. Nature's ordering is dramatically different from the precisely periodic arrays produced from high precision fabrication approaches. In vivo, the organization of the extracellular matrix (ECM) varies dramatically in its structural arrangement, content, texture, and fiber bundle thickness. For example, collagen, the main structural component in ECM, form self-similar fibrils (20-100 s of nm), which in turn form bundles and fibers across several orders of magnitude. (Pins, G. D. et al. (1997) Biophys. J. 73:2164) While cells in vivo experience topographies with features across a vast size range, physiologically comparable cellular environments with length scales that span several orders of magnitude have not been readily simulated by precision micro- or nanofabrication techniques. Achieving such multiscale features typically relies on substantial capital equipment and/or fabrication expertise (Dalby, M. J. et al. (2007) Nat. Mater. 6:997; Engelmayr, Jr., G. C. et al. (2008) Nat. Mater. 7:1003) limiting their accessibility to biological laboratories.